Method and system for purifying or cleansing a gas stream or gaseous body

ABSTRACT

A method and system for eliminating, in whole or in part, contaminants in a gas stream or gaseous body such as air or an exhaust gas or gas emission stream is provided. The method includes the steps of contacting the gas stream or gaseous body with a biocide containing liquid so as to eliminate, in whole or in part, the contaminant(s). The biocide containing liquid is typically an aqueous solution, suspension, or emulsion comprising hydrogen peroxide (H 2 O 2 ) in combination with a catalyst for enhancing the activity thereof, the catalyst preferably comprising a superoxidedismutase formed from the combination of elemental copper (Cu), silver (Ag), manganese (Mn) and zinc (Zn). The method and system find particular application in the combating of sick building syndrome (SBI) and building related illness (BRI).

BACKGROUND OF THE INVENTION

THIS invention relates to a method and system for purifying or cleansinga gas stream or gaseous body containing one or more contaminants.

It is well established that outdoor air pollution can cause serioushuman illness. Air pollution can cause burning eyes and noses, itchyirritated throats as well as breathing difficulties. Some chemicals cancause cancer, birth defects, brain and nerve damage, long-term injury tolungs and even premature death. As a result, protection of the publichealth is a driving force behind the laws and regulations that arebeing, and have been, put into place to clean up the environment.However, ridding outdoor air toxic contaminants has often overlookedindoor air quality (IAQ).

The results of numerous scientific investigations have revealed manyreported outbreaks of what is known as Sick Building Syndrome (SBS) andBuilding Related Illness (BRI) as a direct result of indoor airpollution (IAP) in office and other public access buildings.

SBS is used to describe the situation in which building occupantsexperience acute health and comfort defects that are linked to timespent in the building. BRI is the term used when diagnosable illness andsymptoms are identified and directly attributed to airborne buildingmaterial contaminants.

In modern society, it is believed that most people spend as much as 90%of their time indoors. The US Environmental Protection Agency (EPA) hasindicated that IAP may be between 2–5 times higher than accepted levels,and up to 100 times higher than outdoor pollution levels.

The World Health Organisation (WHO) Committee Report on IAQ suggestedthat 30% of new and re-modelled buildings globally are subject toexcessive complaints of IAQ and have unusually high rates of SBS and/orBRI. For example, according to the SA Singapore embassy, 92% of allabsenteeism in Singapore can be attributed to SBS and/or BRI.

IAQ is rated within the top 5 of the US EPA's most critical globalconcerns alongside ozone depletion, global warming and the like. It hasbeen reported, for instance, that in 1989, the US economy suffered astaggering US $65 bn loss due to SBS and BRI. The absenteeism levels,due to poor health caused by IAP, resulted In this huge productivitydecrease.

SUMMARY OF THE INVENTION

According to the invention, a method of purifying or cleansing a streamof gas or gaseous body containing one or more contaminants, inparticular air or an exhaust gas stream, includes the steps ofcontacting the gas stream or gaseous body with a biocide containingliquid so as to eliminate, in whole or in part, the contaminant(s).

The biocide containing liquid is preferably an aqueous solution,suspension or emulsion of the biocide.

The biocide preferably comprises hydrogen peroxide (H₂O₂) in combinationwith a catalyst for enhancing the activity thereof, the catalystpreferably comprising a superoxidedismutase formed from the combinationof elemental copper (Cu), silver (Ag), manganese (Mn) and zinc (Zn).

The H₂O₂ is typically present in the biocide in an amount of about0.000003% to about 15% v/v, preferably about 0.003% to about 3% v/v, inparticular about 0.3% v/v.

The Cu, Mn and Zn are typically present in an amount of about 100 ppb toabout 1000 ppm, preferably about 3 to 7 ppm, in particular about 5 ppm.

The Ag is typically present in an amount of about 100 ppb to about 1000ppm, preferably about 3 to 9 ppm, in particular about 7 ppm.

The liquid biocide is preferably provided in the form of a fine spray ormist.

The method is preferably used to purify the air in an air conditioningunit of a building such as an office block, house, hospital, shoppingmall, stadium, or the like, a vehicle such as a motor vehicle, bus,truck, ship or train, an aircraft or the like, in mines and otherunderground environments or an exhaust gas or other gas emission from anindustrial factory or the like.

The invention extends to a system for purifying a gas stream or gaseousbody, the system including a gas purifying unit arranged to bring aliquid biocide into contact with a gas stream or gaseous body passingthrough the unit in order to eliminate, in whole or in part,contaminants in the gas stream or gaseous body.

The method and system find particular application in the elimination ofcontaminants selected from inorganic contaminants such as CO, NO₂ andSO₂, organic contaminants such as formaldehyde, hexane and acetone,particulate matter such as dust particles and smoke particles, andmicroorganisms such as viruses for example influenza, small pox and thelike, bacteria, for example legionella and other airborne bacteria, andfungi or their spores, in particular anaerobic microorganisms.

The method and system are preferably used in the combating of sickbuilding syndrome (SBI) and building related illness (BRI).

An embodiment of the invention is described in detail in the followingpassages of the specification which refer to the accompanying drawings.The drawings, however, are merely illustrative of how the inventionmight be put into effect, so that the specific form and arrangement ofthe features shown is not to be understood as limiting on the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompany drawings in which:

FIG. 1 is a schematic side view of a gas purification system of theinvention; and

FIG. 2 is a cross-sectional view on the line 2—2 of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention provides a method and system for eliminating, in whole orin part, contaminants in a gas stream or gaseous body such as air or anexhaust gas or gas emission stream.

Referring to FIG. 1 of the drawings, a gas purification system 10 of theinvention is shown schematically. The system 10 consists of a scrubberunit 12, as shown more clearly in FIG. 2, a liquid collection unit 14and an air dryer unit 16 (optional), all in gas flow communication withone another.

The scrubber unit 12 includes a plurality of spray nozzles 18 forintroducing a fine spray or mist 20 of a biocide solution, suspension oremulsion into the scrubber chamber 22 thereof. As air or other gascontaining contaminants passes through the scrubber 12, in the directionof the arrows in FIG. 1, it contacts the spray or mist. As thecontaminants in the gas or air stream come into contact with the finemist or spray, they are taken up by the spray or mist droplets and henceremoved from the air stream. In addition, the biocide acts to kill themicro-organisms. The biocide solution, typically including water as thecarrier, collects under normal gravitational forces in the collectionunit 14 whereafter it flows through outlet conduit 24 and is pumped intoa filter unit 26 by a pump 28. The contaminants in the solution areremoved in the filter 26 whereafter the water is pumped into the waterfeed tank 30. A biocide feeder 32, typically in the form of a dripsupply tank, feeds biocide into the water in the tank 30 before it ispumped via the conduit 34 into the scrubber unit 12. The collection unit14 includes a water separator 36 at a front end 38 thereof forseparating excess water droplets as the air stream exits the collectionunit 14. The decontaminated air passing from the collection unit 14 mayhave a relatively high relative humidity, in which case it is optionalto pass it through a heating chamber or dryer unit 16 before continuingthrough the rest of the air conditioning system.

It is envisaged that the method and system of the invention can be usedto eliminate, in whole or in part, a number of contaminants includinginorganic contaminants such as CO, NO₂ and SO₂, organic contaminantssuch as formaldehyde, hexane and acetone, particulate matter such asdust particles and smoke particles, and microorganisms such as virusesfor example influenza, small pox and the like, bacteria, for examplelegionella and other airborne bacteria, and fungi or their spores, inparticular anaerobic micro-organisms. The combination of biocide, whichacts on the micro-organisms, and the fine spray, which acts to removeparticles out of the air, are believed to provide an effective air orgas purification method and system.

In order to evaluate the efficacy of the system and method of theinvention, the applicant retained the services of an independent, fullyaccredited testing company (Environmental Science Service ConsultantsESSC) to conduct tests on air containing a number of differentcontaminants. In terms of the methodology, the following pollutants wereintroduced into the air.

-   -   Inorganic gasses: CO, NO₂, SO₂;    -   Organic gasses: formaldehyde, hexane and acetone;    -   Particulate matter: dust of various particle sizes and tobacco        smoke; and    -   Micro-organisms.

The tests were carried out using a prototype which was built as aself-contained, re-circulatory unit housing +/−12 m³ of air volume.Airflow through the prototype was maintained at +/−0.5 m³/s at a speedof +/−2 m/s, producing a 6 second air change. This allowed for theproduction of a ten air change cycle every minute, forming a 1 minute=1hour ratio. Thus, for every minute that the unit circulated the air, itwas equivalent to 1 hour in real time. Hence, 24 minute exposure timeequates into one day or a 24 hour period.

The results of the tests are set out below.

TABLE 1 Inorganic contaminants elimination per 24 hour periodCONTAMINANT PERCENTAGE ELIMINATION Sulphur dioxide (SO₂)  58% Carbonmonoxide (CO)  76% Oxygen (O₂) 0.5% increase Nitrogen dioxide (NO₂)  91%elimination Carbon dioxide (CO₂) Pending

TABLE 2 Organic contaminants elimination per 5 hour cycle PRE- POST- RE-TEST TEST DUCTION PERCENTAGE CONTAMINANT (ppm) (ppm) (ppm) ELIMINATIONFormaldehyde — — — Pending Hexane 1825.6 1125  −700.6 38.3% Acetone2941.2 366 −2904.6 98.75%

TABLE 3 Particulate material CONTAMINANT PERCENTAGE ELIMINATION Finedust particles 99.9% Coarse dust particles 99.9%

In addition to the above contaminants, bacterial microbes from toiletwater of various contamination degrees were brought into contact withthe biocide solution in one passage of airflow through the system and a99.9% elimination was obtained.

In the light of the above test results, it is believed that the methodand system of the invention are capable of eliminating, at least inpart, micro-organisms and harmful gasses that cause sick buildingsyndrome and related illness. The system is relatively inexpensive tomanufacture and the chemical compounds for the biocide are readilyavailable and cost effective. The chemicals used are human-safe,non-toxic and provided in quantities which are well below OSHAregulations.

1. A method of purifying or cleansing a stream of gas or a gaseous bodycontaining one or more contaminants, comprising the steps of contactingthe gas stream or gaseous body with a biocide containing liquid so as toeliminate, in whole or in part, the contaminant(s) wherein the biocidecomprises hydrogen peroxide (H₂O₂) in combination with a catalyst forenhancing the activity thereof and the catalyst comprises asuperoxidedismutase formed from the combination of elemental copper(Cu), silver (Ag), manganese (Mn) and zinc (Zn).
 2. A method accordingto claim 1, wherein the stream of gas is an air stream or an exhaust gasstream.
 3. A method according to claim 1, wherein the biocide containingliquid is an aqueous solution, suspension or emulsion of the biocide. 4.A method according to claim 1, wherein the biocide comprises about0.000003% to about 15% v/v H₂O₂, and about 100 ppb to about 1000 ppmeach of Cu, Mn, Zn and Ag.
 5. A method according to claim 4, wherein thebiocide comprises about 0.003% to about 3% v/v H₂O₂, about 3 to 7 ppmeach of Cu, Mn and Zn, and about 3 to 9 ppm Ag.
 6. A method according toclaim 5, wherein the biocide comprises about 3% v/v H₂O₂, about 5 ppmeach of Cu, Mn and Zn, and about 7 ppm Ag.
 7. A method according toclaim 1, wherein the liquid biocide is provided in the form of a finemist or spray.
 8. A method according to claim 1, wherein the method isused to purify the air in an air conditioning unit of a building,vehicle, an aircraft, in mines, and other underground environments or anexhaust gas or other gas emission from an industrial factory.
 9. Amethod according to claim 1, wherein the contaminants are selected fromthe group consisting of inorganic contaminants, organic contaminants,particulate matter and microorganisms.
 10. A method according to claim7, wherein the contaminants are selected from the group consisting ofCO, NO₂, SO₂, formaldehyde, hexane, acetone, dust particles, smokeparticles, viruses, bacteria, and fungi or their spores.
 11. A methodaccording to claim 1 for use in combating sick building syndrome orbuilding related illness.